Development and validation of Hands-Off Detection function for steering wheel for the CEPS system with a torque sensor

Hands-off detection (HOD) for steering wheel is a technique used in the Advanced Driving Assistance System, which plays an important role in driving safety. However, low-cost solutions to HOD are prone to a high false alarm rate as it regards the torsion bar torque obtained by the torque sensor as the driver torque. To solve this problem, a Column Electric Power Steering (C-EPS) system is taken as the research object in this paper to design a specific model of HOD. Firstly, the dynamic model of steering wheel is constructed, and the unknown parameters in this model are obtained through the sweep test of the assisted motor. Secondly, a discrete extended state observer and a discrete sliding mode observer are developed by taking the driver torque as a state variable, and the torsion bar torque and the motor angle as the input variables. Then, the methods of observer parameters adjustment are proposed to effectively observe the driver torque. Thirdly, to avoid the influence of the disturbance torque transferred from the tire-road contacts on the HOD, a method for estimating road conditions is presented, and the torque threshold for HOD is adjusted automatically according to the road conditions and the vehicle speed. The status of HOD can be obtained from the driver torque and the torque threshold. Both simulation tests and real-vehicle verifications were conducted to demonstrate the reliability and effectiveness of the proposed algorithm. In addition, a fault-tolerant detection mechanism is proposed accordingly. If the angle of steering wheel or the motor cannot be detected, the status of HOD can be obtained by analyzing the ratio of low-frequency energy to high-frequency energy of torsion bar torque. To sum up, the model proposed in this paper meets the specific requirements of HOD, while taking into account both cost-effectiveness and safety performance.